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LTC3405AES6#TRMPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16
4
LTC3405A
3405afa
R
DS(ON)
vs Temperature
Dynamic Supply Current
Dynamic Supply Current
vs Temperature
Switch Leakage vs Temperature
Switch Leakage vs Input Voltage
TEMPERATURE (°C)
–50
R
DS(ON)
(Ω)
1.2
1.0
0.8
0.6
0.4
0.2
0
25 75
–25 0
50 100 125
3405A G11
SYNCHRONOUS SWITCH
MAIN SWITCH
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
SUPPLY VOLTAGE (V)
2
DYNAMIC SUPPLY CURRENT (µA)
1600
1400
1200
1000
800
600
400
200
0
34 56
3405A G12
V
OUT
= 1.8V
I
LOAD
= 0A
PULSE SKIPPING MODE
Burst Mode OPERATION
TEMPERATURE (°C)
–50
DYNAMIC SUPPLY CURRENT (µA)
600
500
400
300
200
100
0
25 75
–25 0
50 100 125
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0A
3405A G13
PULSE SKIPPING MODE
Burst Mode OPERATION
TEMPERATURE (°C)
–50
SWITCH LEAKAGE (nA)
160
140
120
100
80
60
40
20
0
25 75
–25 0
50 100 125
V
IN
= 5.5V
RUN = 0V
3405A G14
MAIN SWITCH
SYNCHRONOUS
SWITCH
INPUT VOLTAGE (V)
0
SWITCH LEAKAGE (pA)
60
50
40
30
20
10
0
1
234
3405A G15
56
RUN = 0V
MAIN SWITCH
SYNCHRONOUS
SWITCH
SW
5V/DIV
V
OUT
100mV/DIV
AC COUPLED
I
L
100mA/DIV
3405A G16
5µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
20mA
SW
5V/DIV
V
OUT
10mV/DIV
AC
COUPLED
I
L
100mA/DIV
3405A G17
500ns/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
20mA
RUN
2V/DIV
V
OUT
1V/DIV
I
L
200mA/DIV
3405A G18
100µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
=
250mA
3405A G19
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0mA TO 250mA
PULSE SKIPPING MODE
TYPICAL PERFOR A CE CHARACTERISTICS
UW
(From Figure 1a Except for the Resistive Divider Resistor Values)
Burst Mode Operation
Pulse Skipping Mode Operation
Start-Up from Shutdown
Load Step
5
LTC3405A
3405afa
UU
U
PI FU CTIO S
RUN (Pin 1): Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
V
IN
(Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
V
FB
(Pin 5): Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.
MODE (Pin 6): Mode Select Input. To select pulse skip-
ping mode, tie to V
IN
. Grounding this pin selects Burst
Mode operation. Do not leave this pin floating.
3405A G20
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA TO 250mA
PULSE SKIPPING MODE
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
3405A G21
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 20mA TO 250mA
Burst Mode OPERATION
3405A G22
40µs/DIV
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 0mA TO 250mA
Burst Mode OPERATION
V
OUT
100mV/DIV
AC
COUPLED
I
LOAD
200mA/DIV
I
L
200mA/DIV
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Load Step Load Step Load Step
(From Figure 1a Except for the Resistive Divider Resistor Values)
6
LTC3405A
3405afa
FU CTIO AL DIAGRA
U
U
W
+
–
+
–
+
–
+
–
OVDET
EA
+
–
I
RCMP
+
–
I
COMP
5
1
RUN
OSC
SLOPE
COMP
OSC
FREQ
SHIFT
0.8V
0.85V
0.8V REF
SHUTDOWN
OV
0.4V
0.65V
SLEEP
V
IN
V
FB
6
MODE
EN
BURST
V
IN
S
R
RS LATCH
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
ANTI-
SHOOT-
THRU
Q
Q
5Ω
4
SW
3
GND
3405A BD
2
OPERATIO
U
(Refer to Functional Diagram)
Main Control Loop
The LTC3405A uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET) switches
are internal. During normal operation, the internal top
power MOSFET is turned on each cycle when the oscillator
sets the RS latch, and turned off when the current com-
parator, I
COMP
, resets the RS latch. The peak inductor
current at which I
COMP
resets the RS latch, is controlled by
the output of error amplifier EA. The V
FB
pin, described in
the Pin Functions section, allows EA to receive an output
feedback voltage from an external resistive divider. When
the load current increases, it causes a slight decrease in
the feedback voltage relative to the 0.8V reference, which
in turn, causes the EA amplifier’s output voltage to in-
crease until the average inductor current matches the new
load current. While the top MOSFET is off, the bottom
MOSFET is turned on until either the inductor current
starts to reverse, as indicated by the current reversal
comparator I
RCMP
, or the beginning of the next clock
cycle.
Comparator OVDET guards against transient overshoots
>6.25% by turning the main switch off and keeping it off
until the fault is removed.
Burst Mode Operation
The LTC3405A is capable of Burst Mode operation in
which the internal power MOSFETs operate intermittently
based on load demand. To enable Burst Mode operation,
simply connect the MODE pin to GND. To disable Burst
Mode operation and enable PWM pulse skipping mode,
connect the MODE pin to V
IN
or drive it with a logic high
(V
MODE
> 1.5V). In this mode, the efficiency is lower at
light loads, but becomes comparable to Burst Mode
operation when the output load exceeds 25mA. The ad-
vantage of pulse skipping mode is lower output ripple and
less interference to audio circuitry.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P16

LTC3405AES6#TRMPBF

Mfr. #:
Buy LTC3405AES6#TRMPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 300mA, 1.5MHz Syn Step-dwn convtr
Lifecycle:
New from this manufacturer.
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